1. Technical Field of the Invention
This invention broadly relates to the treatment of a subsurface earth formation which is penetrated by a borehole. The invention further relates to a method of decreasing the rate of flow of water from a subterranean formation into a borehole which penetrates the formation. This invention more specifically pertains to the introduction of a polymerizable monomer and a crosslinking monomer into a water-containing subterranean formation penetrated by a wellbore and causing the monomer to form a gel in the formation. The polymerization is produced by using a temperature activated compound whereby the polymerization is predictable, reproducible and not affected by oxidation/reduction reactions.
2. Related Art and Problems Solved
When performing various types of operations below the surface of the earth a problem often encountered which interferes with the operation is the undesirable flow of water from a subsurface formation into a work space or volume which penetrates the formation. Such operations can include, but are not limited to, mining operations, foundation construction, road and bridge construction, oil production and similar operations which require excavation into or penetration of earth structures having permeabilities conducive to the flow of water.
The related problem of terminating, or at least reducing, such undersireable flow of water has been attempted to be solved by various means. The solutions attempted have involved, among other things, pumping unwanted water from the work space, erecting barriers, e.g., a casing, at the interface between the space and the formation to prevent the flow of water from the formation into the work space and decreasing the permeability of the formation itself by introducing a material, e.g., a grout, into the formation.
It is well known that both oil and water are produced during the ordinary recovery of oil from a subterranean formation. If the ratio of water to oil, i.e., the water-oil ratio or WOR, is low, then the produced water can be handled and disposed of in a manner which will not unreasonably reduce the economic benefits derived from the produced oil. In such instances, water control can simply involve pumping the water from the well and storing or otherwise disposing of it in some acceptable fashion. However, if the WOR is so high that the various costs of pumping, handling, storing and disposing of the produced water exceeds the economic benefits of the produced oil, then the well is either abandoned or an alternate water control technique is employed.
One alternate water control method is disclosed by McLaughlin in U.S. Pat. No. 3,334,689, wherein an aqueous solution of a polymerizable composition containing a monoethylenically unsaturated acrylate monomer and a crosslinking agent are injected into the formation producing the water. The monomer and crosslinking agent are caused to form a stable crosslinked gel in the formation to thus reduce the water permeability of the formation and thereby terminate or at least decrease the rate of flow of water from the formation.
McLaughlin, in U.S. Pat. No. 3,490,533, discloses injecting into a subterranean formation an aqueous solution of a polymerizable monomer having dissolved therein a polymerization catalyst, i.e., an initiator, having a latent period. The monomer polymerizes in the formation after the latent period of the catalyst has expired. McLaughlin describes the product of the polymerization as a viscous polymer solution. In the practice of the invention, McLaughlin discloses the use of monomers having at least one carbon-to-carbon double bond to which can be added a crosslinking monomer, such as a diallyl monomer, if polymer crosslinking is desired. McLaughlin discloses that excess crosslinking monomer causes gelation which creates a plug rather than a desired viscous, but still flowable fluid. In other words, McLaughlin discloses that a plug can be formed in the formation if a crosslinking monomer is combined with his polymerizable monomer. McLaughlin, by way of example, thus discloses that a crosslinked polymer can be produced by polymerizing acrylamide in the presence of methylene bisacrylamide or the crosslinking monomers disclosed in U.S. Pat. No. 3,334,689 referred to above.
In each of the prior art methods referred to above, the aqueous solution of polymerizable monomer and crosslinking agent also includes a polymerization initiator. The initiators employed are disclosed to be selected from persulfates, amines and peroxides. Specific initiators known to be employed in existing polymerization systems include sodium persulfate and triethanol amine, potassium persulfate and ammonium persulfate and tertiary butyl hydroperoxide.
The initiators heretofore employed are activated by a number of mechanisms including heat and oxidation/reduction reactions and are well known to be difficult to use because their activation is difficult to control, thus rendering unpredictable the time to produce a gel from the aqueous solution containing the monomer, crosslinker and initiator.
It is thus an object of this invention to produce a crosslinked polymer in a formation by use of an initiator whose activation can be controlled in order to enable the prediction of the time required to produce a gel from an aqueous solution containing a polymerizable monomer, a crosslinking agent and an initiator.